Fuel cells are a kind of power generation apparatus that does not convert chemical energy of a fuel into heat by combustion, but converts the chemical energy into electric energy by an electrochemical reaction in a stack, and may be used to supply to power to small electric/electronic products, particularly, portable apparatuses, as well as supply industrial power, domestic power, and power for driving a vehicle.
A polymer electrolyte membrane fuel cell (or a proton exchange membrane fuel cell) (PEMFC) having the highest power density among the fuel cells has been currently studied mainly as a source supplying the power for driving the vehicle. The PEMFC has a rapid start-up time and a rapid power conversion reaction time due to a low operation temperature.
The PEMFC is configured to include a membrane-electrode assembly (MEA) in which catalyst electrode layers in which an electrochemical reaction occurs are attached onto both sides of a solid polymer electrolyte membrane in which protons move, gas diffusion layers (GDLs) serving to uniformly diffuse reaction gases and transfer generated electric energy, gaskets and fastening mechanisms maintaining air-tightness and appropriate fastening pressures of the reaction gases and a coolant, and bipolar plates moving the reaction gases and the coolant.
When a fuel cell stack is assembled using the configuration of the unit cell described above, a combination of the membrane-electrode assembly and the gas diffusion layer, which is a main component, is positioned at the innermost side of the cell. The membrane-electrode assembly has the catalyst electrode layers, that is, an anode and a cathode, formed on both surfaces of the solid polymer electrolyte membrane and having catalysts applied so that hydrogen and oxygen may react each other, and the gas diffusion layers, the gaskets, and the like, are stacked onto outer surfaces of the anode and the cathode.
The bipolar plates supplying the reaction gases (hydrogen corresponding to a fuel and oxygen or air corresponding to an oxidizing agent) and having flow fields through which the coolant passes are formed outside the gas diffusion layers.
After a plurality of unit cells having the configuration described above are stacked, current collectors, insulating plates, and end plates for supporting the stacked cells are coupled to the outermost side, and the unit cells are repeatedly stacked and fastened to one another between the end plates to constitute the fuel cell stack.
In order to obtain a potential required in an actual vehicle, the unit cells should be stacked by the required potential, and the stack is formed by stacking the unit cells. A potential generated in one unit cell is about 1.3V, and a plurality of cells are stacked in series with one another in order to generate power required for driving the vehicle.
Therefore, when performance deterioration or a fault occurs in any one of the unit cells constituting the fuel cell stack, entire performance of the fuel cell stack is deteriorated, such that a stable operation is not provided.
In a technology for diagnosing a state of a fuel cell stack according to the related art, the state of the fuel cell stack is diagnosed using only an impedance of the fuel cell stack rather than impedances of each channel including a predetermined number of cells, and it may not be thus detected whether or not abnormity is generated in a channel unit.
Particularly, in the technology for diagnosing a state of a fuel cell stack according to the related art, a cell into which foreign materials are introduced, a frozen cell, a cell having an insufficient humidity amount, a cell having an excessive humidity amount, and the like, may not be detected, and a mixed state in which a cell having an insufficient humidity amount and a cell having an excessive humidity amount coexist with each other may not be diagnosed.